Current-collecting device



April 1 1924. 1,488,575

C. F. WAGNER CURRENTCOLLECTING DEVICE l Filed July 5. 1922 1 l l l I l I Patented Apr. l, 1924.

UNITED STATES 1,488,575 PATENT OFFICE.

CHARLES F. WAGNER, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, .A CORPORATION OF PENNSYL- VANIA.

Application iugm July 5,

To all whom t may concem:

yBe it known that I, CHARLES F. VVAGNEP., a citizen of the United States, and a resident of Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented a new and useful Improvement in Current-Collecting Devices, of which the following is a specification.

My invention relates to current-collecting devices and it has particular relation vto means for equalizing the current traversing the several brushes of a dynamo-electric machine.

Heretofore, it has been observed that the C current-collecting brushes for dynamo-electric machines, andparticularly machines of the rotary converter type which employ a large number of brushes connected in parallel relation and which co-operate with a single collector ring, are subjected to `unequal wear. Extensive experiments have, therefore, been conducted for the purpose of determining the cause of theinequality in brush wear.

As a result of investigation it has been ascertained that one of the principal causes of unequal brush wear is the unequal flow of current through the several brush members which causes the decomposition of the brushes subjected to excess current flow. The inequality of current flow in the different brushes may, in turn, be attributed to several causes, such as the formation of a film of air of substantially wedge shape between the brush member and the collector ring; carbon deposits on the contact surfaces of certain of the brushes; unequal pressures exerted by the brush springs; uneven contact surfaces of the brush members; inequality in the chemical constituents of the contact surfaces and particularly those of the brush members; the unstable volt-ampere characteristics of the brushes in general and the eect of lnon-uniform external conditions, such as the resistance and the reactance of the paths of the current from the brushes, as in the brush-holder stand to which the brush shunts are electrically connected.

One of the objects of my -invention is to provide means for overcoming the difference in impedance existing in the current aths of a plurality of brushes connected 1n parallel relation and to stabilize or bal- .ance the flow of current therethrough by CURRENT-COLLECTING DEVICE.

1922. Serial No. 572,915.

inserting a resistor element in series with the individual brushes.

Another object of my invention is to provide a resistor element, of the character described, that may be quickly and easilyY connected in the brush circuits of a dynamoelectric machine without changing the structure thereof, and that is so constructed and arranged as to occupy but a small space.

In the accompanying drawing:

Figure l is a side elevational view of a brush holder provided with a resistor element constructed and arranged in accordance with my invention.

Fig. v2 is a detail perspective view of the resistor element illustrated in Fig. l.

Fig. 3 is a view of another form of my invention.

Fig. 4 is a diagrammatic view illustrati ing the difference between the volt-amperage characteristics of a brush operating respectively with and without a resistor element.

Referring to the drawing, a brush holder of standard construction is shown as comprising a brush box l which is adapted to receive and retain a brush member 2 for co-operation with a collector ring 3. The brush box lis provided with a vertically extending' portion 4 which is secured to a bracket element 5 by means of a bolt 6.

The member 4 is provided with a serrated surface 7 for co-operation with a similar surface formed on the bracket element 5, and it vfunctions to maintain the brush holder securely ink its adjusted position. The element 4 is insulated from the bracket element 5fby means of a strip of insulating material 8 which is clamped between the coacting serrated surface 7 and also by means of an insulating spacing washer 9 disposed between the bolt 6 and the outer surface of the member 4. The bracket element 5 is mounted upon a stud 10 carried by the frame of the dynamdelectric 'mal chine, not shown.

`The upperv portion of the bracket 5 is provided with a vertically extending lug 1l to which a resistor element, indicated, as a Whole, at 12, is secured at one end by means of screws 13. The resistor element 12 is preferably of sinuous configuration, as is best illustrated in Fig. 2, whereby a relatively long current path is obtained therethrou h without materially increasing the overal? dimensions of the resistor element. The outer end of the element 12 is provided with a downwardly extending rod or bar 141 to the loiver extremity of which a shunt attachment 15 of t-he brush member 2 is secured, as indicated at 16.

In Fig. 3 is illustrated another `form of my invention in which the resistor element 12 is bent upon itself into substantially inverted U-shape, the legs of which are formed with supporting feet 1T and 18. The foot 17 of the resistor element is electrically connected to the upper surface of the bracket member 5, as at 19. The foot 18 is also secured to the bracket 5 at 2O but is insulated therefrom by means of spacing Washers 21 of insulating material. The foot portion 17 overhangs the edge of the bracket 5 and is provided vvith an eye portion 22 to which the shunt attachment 15 of the brush member is secured by means of a bolt 23.

The effect of the above described construction may be best explained with reference to Fig. et of the drawings, which diagrammatically illustrate the volt-ampere characteristics of a brush operating with and Without a resistor element. From an inspection of the figure referred to, it will be observed that the voltage drop across a metallized carbon brush increases but slightly .with a large increase in current, as indicated at Q1. This voltage drop across a single brush is insufficient to function as a regulating voltage to maintain the currents through the several associated brushes substantially equal.

A resistor element 12 is, therefore, connected in series with each of the individual brushes, and the respective brush and resistor elements are in turn, connected in parallel relation. A greater regulating voltage is. therefore, obtained by reason of the fact that, if more current tends to flow through one of the brushes and its resistor than through another similar group of elements, the potential difference established across the first resistor, being proportional to the current of greater value, Will be suffiient. as illustrated by the curve 25, to functionas ay regulating voltage, to effect an increased flow of current through the brush and resistor being traversed by the lesser current.

The regulating action of this potential difference established across the brush and the resistor carrying the larger current is eHected by reason of the fact that a greater potential difference is available to cause more current to traverse the other'brush and resistor than would be caused by the relatively small potential difference across the brush alone.

By means of thel constructions above set forth, an accurate regulation of current flow through the brushes is obtained and the destructive action of excess currents traversing the brushes is materially diminished.

l claim as my invention:

l. A current-collecting device. comprising a brush holder adapted to support a brush for co-operation with a rotating contact member, and a. resistor element carried by said brush holder and connected in series with said brush.

Q. A current-collecting device comprising a brush holder adapted to support a brush for co-operation with a rotating contact member, and a sinuous resistor element carried by said brush holder and connected in series with said brush.

A current-collecting device comprising a brush holder adapted to support a brush for co-operation with a rotating contact member, and a resistor element carried by said brush holder and connected in series ivith said brush, said resistor element being so formed that the current path therethrough is of greater length than the overall length of said element.

4. A current-collecting device comprising a brush holder adapted to support a brush for co-operation With a rotating contact member, and a` resistor element carried by said brush holder and connected in series with said brush, said resistor element being of non-laminated construction and bent upon itself to provide a current path of greater length than the overa-ll length of said element.

5. A current-collecting device comprising a brush holder adapted to support a brush for co-operation with a rotating contact member and a resistor element of non-laminated construction and sinuous configuration having one end thereof secured to said brush holder and the other end electrically connected to said brush member.

6. A current-collecting device comprising a brush holder adapted to supporta brush for co-operation with a rotating contact member, anda resistor element consisting of a relatively flat stra-p bent upon itself and secured at one end to said brush holder and at the other end electrically connected to said brush.

In testimony whereof, I have hereunto subscribed my naine this 28th day of June 1922.

CHARLES F. WAGNER. 

